The present invention relates to a display device, particularly to the cantilevered mounting of a deflection unit on the external surface of a cathode ray tube envelope.
When mounting a deflection unit sometimes referred to as a yoke, it is known to provide a moulded plastic former into which saddle coils are positioned. Additional saddle coils are disposed on the external surface of the former. A ferrite cone is placed about the outer coils. The deflection unit is then placed on a master tube and a test picture is displayed on the display tube screen. The positions of the ferrite cone and the outer windings are adjusted so that the test picture is correct and a quick setting epoxy resin is used to bond the relevant parts together.
Other proposals for mounting deflection units are disclosed in U.S. Pat. Nos. 3,986,156 and 3,939,447 and German Auslegeschrift No. 26 55 960. In the case of U.S. Pat. No. 3,986,156 an annular platform is bonded onto the external surface of the tube cone. A housing is mounted on the deflection unit. At positions disposed at 90.degree. of rotation about the Z-axis of the display tube, rigid members are disposed between and connect the deflection unit to the platform. Once the position of the deflection unit has been adjusted the rigid members are either bonded or ultrasonically welded in position. Such a mounting arrangement has three strong degrees of freedom and three weak degrees of freedom.
U.S. Pat. No. 3,939,447 discloses three embodiments of a yoke mounting means. In the simplest of these three embodiments the deflection unit is mounted in an annular housing which four cantilever springs extending threfrom. This assembly is placed on the neck of the display tube so that the free ends of the springs are in direct contact with the conical portion of the tube envelope. Each spring has a hollow post thereon which serves as a conduit for adhesive. After the deflection unit has been adjusted then the springs are bonded to the conical portion by adhesive introduced through the hollow posts. Optionally auxiliary coil springs may be attached between the posts and the display tube mounting means to minimize any shearing force between the cantilevered springs and the conical portion of the envelope caused by the pressure of the cantilevered springs which, due to the adjustment of the deflection unit, are under varying degrees of distortion. The use of adhesives to secure the springs to the envelope has a number of disadvantages with respect to the speed of fixing and the reliability of the respective joints.
Auslegeschrift No. 26 55 960 discloses a defection unit mounting system comprising a supporting ring bonded onto the conical surface of the display tube envelope. Flexible arms extend from the deflection unit and engage the supporting ring with a knife edge contact. The position of the deflection unit is adjusted to its desired position by flexing the arms and once the optimum position has been reached the knife edge contacts of the arms are ultrasonically welded to the supporting ring and a potting compound is introduced into the space between the tube neck and the end of the deflection unit.
These methods of deflection unit mounting do not lend themselves to being easily mechanised. For mechanisation of the deflection unit mounting it is necessary to be able to mount the deflection unit on the tube neck, adjust the unit to its optimum position to give a proper image and to fix the unit in this optimum position very rapidly. The mounting arrangement should be such as to provide shock resistance, thermal stability over the expected working life of the tube and only 6 degrees of freedom.